Optimization Of FCC Catalytic Dry Gas Recovery And Concentrated Ethylene Extraction Process

With the slowdown of oil consumption and the growth of chemical product demand in China,it has been an irresistible trend for oil refining enterprises to transform and upgrade from "fuel" to "chemical".At present,catalytic cracking/cracking is an important process for oil refining to chemical industry.China’s FCC dry gas production is 5.2 Mt/a,of which about 1.0Mt/a ethylene resource is wasted.Therefore,how to efficiently recover ethylene from catalytic dry gas has become the focus of the refining industry.At present,the shallow cold oil absorption separation method is widely used in the recovery process of catalytic dry gas,but it has the disadvantages of high energy consumption and low ethylene yield.Aiming at this problem,this paper analyzed the process of catalytic dry gas recovery to improve the ethylene concentration,proposed an improvement method for the process,and carried out multi-objective optimization of process parameters to achieve low energy consumption and high ethylene yield.Based on Aspen Plus platform,a catalytic dry gas recovery and separation process of ethylene was established in this paper.The 110 kt/a shallow cooling oil absorption catalytic dry gas recovery ethylene plant in Qilu Petrochemical was taken as the benchmark,and the accuracy of the model was verified by comparing with the calibration values.Through the simulation results,the energy consumption and product distribution of the device were analyzed,and the economy and applicability of other catalytic dry gas separation processes were evaluated,which provided background support and optimization direction for the process.Through the study on the single stage equilibrium process of typical separation process distillation and absorption process,it is determined that the absorption process is more suitable for separation,and the best absorbent is isobutane.According to the research results of single stage separation,two sets of improved processes are proposed.The first set is to remove the reboiler at the bottom of the original absorption tower,and add flash evaporation tank to the absorption tower and desorption tower.The second set is to add stripper between the absorber and desorption tower.According to the product and yield comparison of the two schemes,the final improved process was determined to add stripper between the absorber and desorption tower.Compared with the benchmark process,the energy consumption was saved by about14.14% and the recovery rate was 94.08%.To select the best scheme for the process conditions of the improved process,multiobjective optimization was carried out for the improved process.With the annual total cost of TAC,Q and ethylene yield of eta energy consumption as objective function,based on the second generation of the sorting genetic algorithm(NSGA-Ⅱ)puts forward multi-objective optimization procedures in the MATLAB software,on the premise of meet the constraint conditions,results show that the absorbent flow rate and reflux ratio on the TAC biggest desorption tower,and the minimum TAC optimization scheme and the minimum energy consumption optimization scheme.The multi-objective optimization scheme was selected by normalizing the Pareto front of TAC and yield.Compared with the benchmark process,the multi-objective optimization scheme reduced TAC by 9.43% and improved recovery rate by2.14% and energy consumption decreased by 15.5%.The results show that the new process significantly saves energy consumption and TAC.